Catalytic process and products thereof



Patented June 25, 1946 UNITED STATES PATENTOFFICE} Mark W. Farlow andFrank K. Signaigo, Wil

mington, Del., assignors to E. I. du Pont de Nemours & Company,Wilmington, Del., a cor poration of Delaware No Drawing.

15 Claims. 1

This invention relates to thiols and a process for their preparation.

This application is a continuation-in-part of copending applicationSerial No. 289,580, filed August 11, 1939.

Within recent years organic sulfur compounds have become of considerableimportance as industrial chemicals, particularly in the fields ofinsecticides, surface-active agents, rubber chemicals, andpharmaceuticals. As a starting point for the preparation of many suchcompounds, the thiols are of prime importance. These may be oxidized todisulfides and sulfinic and sulfonic acids. They may be reacted alsowith organic halogen compounds to form thio ethers which on oxidationare converted to sulfoxides and sulfones. Another class of sulfurcompounds derived from thiols are the thioacetals and thioketals. Thisinvention has as its object a process for the production of thiols.Another object is an economical process for the production of thiolsadaptable to large-scale operation. Other objects will be apparentfromthe following description oi the invention.

These objects are accomplished by the following invention whichcomprises catalvtically hydrogenating an organic compound having athioaldehyde group or a sulfhydrate or polymer thereof. Alternatively,an' organic compound containing an aldehyde group or a group that ishydrolyzable to an aldehyde group is catalytically hydrogenated in thepresence of hydrogen sulfide.

In practicing this invention it is usually more convenient to combineinto a single operation the formation and hydrogenation of thethioaldehyde. To accomplish this, an aldehyde is charged into ahydrogenation autoclave together with sulfur as a source of hydrogensulfide and a sulfactive hydrogenation catalyst. The autoclave is thencharged with hydrogen at super-atmospheric pressure and agitated andheated to a temperature at which reaction proceeds at a suitable rate,usually in the neighborhood of 150 C. After the'reaction is complete asevidenced by thecessation of hydrogen absorption, the autoclave iscooled and the product is filtered from the catalyst. The thiol may thenbe isolated or purified, usually by distillation. The followin examplesshow in greater detail the practice of this invention in'several of itsmodifications. The amounts of materials referred to are parts by weight.l

v v "Example I A sulfactive hydrogenation catalyst is prepared asfollows: A solution of 240 parts of sodium sulfide nonahydrate and 64parts of sulfur in 1500 parts of water is added with stirring to aApplication September 19, 1940 Serial No. 357,419

solution of 238 parts of cobalt chloride hexahydrate in 1700 parts ofwater. The black precipitate is filtered with suction and washedsubstantially free from soluble salts with water. Since the dry catalystoxidizes spontaneously in air with resulting loss in catalytic activityit is protected from air by being stored andused in a liquid medium.Suitable liquids are water, a1- cohols, ethers, hydrocarbons and organicacids. The presence of acids during the hydrogenation process frequentlyleadsto more: rapid conversion of carbonyl compounds to thiols so thatit is convenient to wash the catalyst with'an acid such as acetic acidand to use the catalyst in the form of a paste with acetic acid. Thiscatalyst is used to convert an aldehyde to a thiol as follows: I I

One hundred parts of commercial heptaldehyde, partsof sulfur, and 55parts of the acetic acid-cobalt polysulfide catalyst paste containing 10parts of cobalt polysulfide are charged into a hydrogenation autoclave.The autoclave is then filled with hydrogen to an initial pressure of1200 lbs/sq. in. and agitated and heated to C. At this temperaturereaction is rapid, as evidenced by the rapid decrease in pressure, andadditional hydrogen is added from time to time to replace that absorbedand to maintain the pressure within the range from 1200 to 2800 lbs/sq.in. After one hour at reaction temperature, the reaction becomes slowerand" th temperature is raised to C. for. an additional hour. The productis rinsed from the cooled autoclave with ether and filtered to separatethe catalyst. The filtrate is then washed-with water to remove theacetic acid, dried over anhydrous sodium sulfate and distilled. Afterremoval of the ether and an intermediate cut, '77 parts ofheptanethiol-l distills over at 90 to 93 C. at 49 mm. pressure. Fifteenp'arts of higher'boiling material remains in the distillation pot. Thedistilledthiol has a refractive index of n=1.4488 and density ofd4=0.8399. It' contains 23.8% of thiol sulfur, which corresponds to apurityof 98% as heptanethiol-l. The conversion ofheptaldehyde to heptanethiol may be formulated as follows:

cat. (1) 8 +H HIS Emomplell A nickel sulfide hydrogenation catalyst isprepared as described in Example I for the cobalt sulfide catalystexcept that an equivalent amount of nickel chloride hexahydrate issubstituted for the cobalt "chloride hexahydrate. Seventy parts ofdistilled heptaldehyde, 36 parts of sulfur, '75 parts of dioxane solventand 17 parts of the acetic acid catalyst paste containing 7 parts ofnickel polysulfide catalyst are charged into a hydrogenation autoclavetogether with hydrogen at an initial pressure of 1000 lb./sq. in. Theautoclave is agitated and heated at 175 C. for 3 hours, during whichtime additional hydrogen is added, the total pressure being maintainedwithin the range from 800 to 1600 lbs./sq. in. The contents of theautoclave are rinsed out with dioxane and filtered to separate thecatalyst. The solution is then blown with nitrogen to remove theunreacted hydrogen sulfide. Titration of an aliquot of the product withstandard iodine solution indicates the yield of heptanethiol-l to be"77% of the theoretical. The pure heptanethiol-l is separated from thesolvents and small amount of by-products by distillation.

Example III One hundred parts of 2-ethylhexanal-1, 60 parts of sulfur,50 parts of acetic acid, and 15 parts of cobalt sulfid catalyst arecharged into a hydrogenation autoclave. The cobalt sulfide catalyst isprepared by bubbling hydrogen sulfide through a methanol suspension offinely divided pyrophoric cobalt metal at room temperature until nofurther sulfldation occurs. The autoclave is charged with hydrogen to apressure of 1000 lbs/sq. in. and agitated and heated to a temperature of150 C. Additional hydrogen is added occasionally to replace thatabsorbed. After 3 hours the initial rapid reaction has subsided, and thetemperature is raised to 175 C. and maintained there for an additional 3hours to insure completion of the reaction. The autoclave is cooled, andthe contents rinsed out with ether and the solution filtered to separatethe catalyst. The crude product is then fractionated from the solventsand there is obtained 96 parts of pure 2-ethylhexanethiol-i and 11 partsof high-boiling residue. The thiol boils at 77 C./17 mm., has arefractive index of n"=1.4541 and density of d4= =0.8467. It contains21.5% of thiol sulfur. Calculated for Cam-18H: 21.9%. The yield is 84%of the theoretical.

Example IV One hundred parts of commercial benzaldehyde, 60 parts ofsulfur and 5 parts of finely divided activated iron ar charged into ahydrogenation autoclave. The iron is prepared by extracting the aluminumwith hot caustic solution from a powdered alloy of equal weights of ironand aluminum. hydrogen to an initial pressure of 1000 lbs/sq. in. andagitated and heated to 150 C. During the period of heating the autoclaveto reaction tem-.

perature the pyrophoric iron reacts with the sulfur to form an activeiron sulfide catalyst. As reaction proceeds, additional hydrogen isadded to maintain the pressure above 1000 lbs./sq. in. After 4 hours theautoclave is cooled and the reaction mixtur is filtered from thecatalyst and distilled at reduced pressure. There is obtained 93 partsof pure phenylmethanethiol boiling at 99 C./33 mm. It has a refractiveindex of na* =1.5729 and density of d4=0.8097. There is also obtained 12parts of high-boiling distillation residue. The yield of thiol is 80% ofthe theoretical. The formation of the catalyst and the The autoclave ischarged with' conversion of benzaldehyde may be formulated as follows:

to the preparation of thiols from aldehydes containing other functionalgroups. This is shown by the following experiments.

Example V One hundred parts of commercial 2-ethylhexenal-i, 60 parts ofsulfur, and parts of cobalt sulfide-acetic acid catalyst pastecontaining 15 parts of cobalt polysulfide are charged into an autoclave,together with hydrogen at an initial pressure of 1000 lbs/sq. in. Theautoclave is agitated and heated to a temperature of 150 to 175 C. for 5hours and the pressure is maintained within the range of 1000 to 2000pounds by the addition of more hydrogen as needed. The contents of thecooled autoclave are then rinsed out with ether and filtered to separatethe catalyst and vacuum distilled. In addition to a foreshot of solventsthe following fractions are obtained:

Thiol Fraction B g t 32 Amount sulfur content Pod: Percent Fraction 2 is2-ethylhexenethiol-1 contaminated with unconverted starting material.Fraction 1 is principally 2-ethylhexanedithiol-L3 or possibly -1,2. Byrefractionation nearly pure 2-ethylhexanedithiol is obtained. It boilsat 131 C. at 27 mm., has a refractive index of nc=1.5042 and contains35.5% sulfur; Calculated for CaH1aS-z:S=36.0%. The formation of thesethiols may be illustrated by the following equations:

cat. S H B B Forty parts of 5-carbomethoxyvaleric aldehyde, 20 parts ofsulfur. and 5 parts of cobalt polysulfide catalyst prepared as describedin Example I and pasted with methanol are charged into an autoclavetogether with parts of methanol solvent. The autoclave is filled withhydrogen to an initial pressure of 800 lbs.'per sq. in. and heatedduring 45 minutes to 160 C. The reaction commences at about C. asevidenced by the decrease in pressure and becomes very rapid at 160', C.After 2.5 hours heating, no further pressure drop is observed and theautoclave is cooled and the contents filtered to separate the catalystand blown with nitrogen to remove the unreacted hydrogen sulfide.Titration of an aliquot of the product with standard iodine solutionindicates the conversion to 5-carbomethoxypentanethiol-1 to be 48% ofthe theoretical. By distillation of the crude product there is obtaineda liquid fraction boiling at 125 to 127 C. at 26 mm. Based on its thiolsulfur content of 10.8%, it is a mixture of unconverted startingmaterial with about 55% of the 5-carbomethoxypentanethiol-1.

Example VII Sixty-six parts of commercial aldol and 48 parts of sulfurare charged into an autoclave together with 66 parts of dioxane solventand 6 parts of cobalt sulfide catalyst pasted with dioxane and preparedas described in Example 1. Hydrogen is admitted to the autoclave to apressure of 1200 lbs. per sq. in. and the autoclave is stirred andheated at 125 C. for 6 hours. During this period hydrogen is added tothe autoclave, the pressure being maintained within the range from 1200to 2000 lbs/sq. in. After filtering the reaction mixture from thecatalyst and removing the excess hydrogen sulfide, titration of analiquot of the product indicates the presence of 0.935

mol of thiol for each 100 grams of aldol charged.

Vacuum distillation of the reaction mixture yields the followingfractions:

Fraction B. P. Pressure Amount 'lhiol sulfur content Mm. Par!!! 28 ON.18 27 41.5%. 81 C 3 13 13.8% (total S =42.4). Residue. 6

Theanalyses and boiling points indicate that fraction 1 is a mixture ofapproximately equal parts of 3-hydroxybutanethiol-l andbutanedithiol-1,3. Fraction 3 is apparently 3-hydroxybutylS-mercaptobutyl sulfide. The dithiol and the sulfide are formed probablyby the addition of hydrogen sulfide and the hydroxybutanethiol,respectively, to crotonaldehyde, followed by conversion of the aldehydegroup to a thiol group.

The crotonaldehyde results from dehydration of some of the aldol.

Example VIII Sixty-five parts of commercial dextrose and 30 parts ofpowdered sulfur are charged into a hydrogenation autoclave, togetherwith 100 parts of water and 6 parts of cobalt sulfide catalyst in theform of an aqueous paste. Hydrogen is admitted to the autoclave to apressure of 130m lbs/sq. in. and the autoclave is agitated and heated to125 C. At this temperature a rapid reaction ensues as evidenced by thedecrease in pressure and more hydrogen is added from time residue. Thecrude product contains 12.2% of thiol sulfur which corresponds to athiosorbitol content of76%.

Eazmple IX The process or this invention is applicable also to theconversion of'hydrolyzable derivatives of aldehydes to the correspondingthiols, as is illustrated by the following experiment. Fourteen parts ofthe solid addition product of lauric aldehyde and sodium bisulfite ischarged into a hydro genation autoclave together with 10 parts of sulfurand 2.5 parts of cobalt sulfide catalyst and 100 parts of water. Theautoclave is heated at a temperature of 160 C. for 3 hours, after whichtime no further decrease in pressure is observed. The reaction mixtureis filtered from the catalyst, acidified and extracted with ether.Evaporation of the ether leaves a residue of '7 parts of a colorless oilcontaining 5 parts of dodecanethiol-1.

The conversion of various aldehydes to the corresponding primary thiolshas been illustrated in the foregoing examples. The process of thisinvention is applicable generally to other compounds having an aldehydegroup. As examples of compounds that may be converted to thiolsaccording to this invention, there may be mentioned saturated aliphaticaldehydes such as formaldehyde and its polymers (paraldehyde).acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde,n-Valeric aldehyde, isovaleric aldehyde, hexaldehyde, caprylic aldehyde,lauric aldehyde; unsaturated aldehydes such as acrolein, methacrolein,tiglic aldehyde, crotonaldehyde, 2-ethyl-3-propyl acrolein, geranial,citronellal; aromatic aldehydes such as toluic aldehydes and cinnamicaldehyde. The aldehyde may contain also other functional groups inaddition to the carbonyl group. Examples of such functional groups arethe ethylenic bond,

1 the acetylenic bond and hydroxyl, ether, amino,

halogen, nitro, and carboxyl groups. Examples of compounds of this classare glycolic aldehyde,

glyoxylic acid, chloral, glyceric aldehyde, diacetonaldehyde, furfural,alpha-pyrrolaldehyde, aldose sugars, chlorobenzaldehyde,salicylaldehyde, nitrobenzaldehyde, ,vanillin, veratric aldehyde,methoxybenzaldehyde, dihydroxybenzaldehyde and the like. Compoundscontaining more than one aldehyde group may also be processed accordingto this invention to yield diand polythiol compounds. Examples ofcompounds of this class are glyoxal, adipic dialdehyde and phthalicaldehydes.

Certain aldehydes form hydrates which are considered to have thegrouping H OH Such hydrates will behave as true aldehydes in the procesof this invention, and their conversion to thiols is likewise a part ofthis invention. Generally, derivatives that. are hydrolyzable tocarbonyl compoundsmay also be converted to the corresponding thiols bythis process. Examples of compounds of this class are the bisulfiteaddition compounds of aldehydes (see Example IX), the aldimines,aldehyde ammonias, hemiacetals (Example VIII) and the hydrazones,semi-carbazones, oximes, and anils of aldehydes.

The normal product obtained by the hydrogenation of an aldehyde in thepresence of hydrogen sulfide according to the process of this inventionis the corresponding thiol in which the mercapto group is attached tothe carbon atom originally forming the carbonyl group. .As explained insome oi the foregoing examples, however, alpha, beta-unsaturatedaldehydes react to form dithiols in addition to the unsaturated thiols.The second mercapto group in the dithiol is formed by addition ofhydrogen sulfide to the double bond.

While not essential in most cases, solvents may be employed in carryingout the hydrogenation process. Examples of solvents that may be used arewater and organic solvents such as hydrocarbons, alcohols, ethers,acids, and the like. In addition to simple solvents the reaction mayalso be accomplished in the presence of such materials as acids,alkalis, ammonia, and amines. The use of acids in the reaction mediafrequently leads to more rapid conversion to thiols.

In the foregoing examples the use of sulfur as a source of hydrogensulfide has been illustrated.

as this is an especially convenient way to generate the desired reagent.However, hydrogen sulfide itself may be charged into the autoclavetogether with the other reactants. Instead of hydrogen sulfide orsulfur, other sulfur compounds that are converted to hydrogen sulfideunder the reaction conditions may be used. Examples of such materialsare sulfur dioxide, ethyl tetrasulfide, carbon bisulfide, and alkali andammonium sulfides. The proportion of hydrogen sulfide to carbonylcompound employed may be varied considerably. However, it is usuallypreferred to employ anexcess of hydrogen sulfide or source of hydrogensulfide over the amount theoretically required.

The process of this invention may be operated over a considerable rangeof temperatures and pressures. Reaction occurs in many case attemperatures as low as 100 0., although usually at a, low rate. As thetemperature is raised, the rate of reaction increases, and, it istherefore preferable to operate at temperatures above 100 C. The uppertemperature limit at which the process may be operated is determinedprincipally by the thermal stability of the compound processed. In mostcases the compounds are stable at temperatures up to at least 200 C. andtherefore it is suitable to operate at temperatures between 100 and.200C. The reaction proceeds well even at low pressure of hydrogen, butinorder to insure a practicable rate of reaction it is desirable tooperate at a hydrogen pressure of at least 100 lbs/sq. in.

As sulfactive catalysts that may be used in carrying out the process ofthis invention. it has been found that certain metal sulfides areespeclally suitable for this purpose since these are not poisoned bysulfur and are at the same time highly active. Examples of these aresulfides of the hydrogenating metals such as chromium, cobalt, copper,iron, lead, molybdenum, nickel, palladium, tin, tungsten, and vanadium.It is preferred, however, to use sulfides of the metals cobalt,molybdenum, nickel, and iron, since these have been found to beespecially active. Such catalysts may be prepared by a variety ofmethods, as, for example, by precipitating the metal sulfide from asolution of a metal salt with hydrogen sulfide, a solution of alkali oralkaline earth metal sulfide or polysulfide, or with emmonium sulfide orpolysulfide. Another method that has been found to yield very activecatalysts is to treat the finely divided .pyrophoric or activated metalsuspended in a liquid medium with sulfide in many cases can be combinedconveniently into a single operation with the hydrogenation reaction forwhich the catalyst is to be used By the term.sulfactive hydrogenationcatalyst" as used herein and in the claims, we mean a catalyst preparedas described in U. 5. Patents Nos. 2,221,804 and 2,230,390, and which isactive for the catalytic hydrogenation of the sulfur in organicmultisulfides, organic sulfur compounds having carbon to sulfurunsaturation, and organic sulfur compounds having sulfur to oxygenunsaturation.

Instead of charging the metal sulfide as such, it may be formed in situby 'placing the finely divided pyrophoric or activated metal into theautoclave together with the other reactants. The sulfur or hydrogensulfide present will convert the metal to the active metal sulfide inthe early stages of the reaction process. The catalyst employed may besubstantially a pure metal sulfide or a combination of metal sulfides.Other I substances may be present also as, for example,

kieselguhr, alumina, magnesia, carbon, and other supporting or promotingmaterials.

As mentioned above, it is especially convenient to form the thioaldehydeand hydrogenate it to the corresponding thiol in a, single operation.However, it is within the scope of this invention to react an aldehydewith hydrogen sulfide by any suitable means and subsequently tohydrogenate the reaction product with a sulfactive hydrogenationcatalyst to obtain the thiol, One method for forming thioaldehydes ortheir polymers is to dissolve the aldehyde in absolute alcohol andsimultaneously to pass streams of anhydrous hydrogen chloride andhydrogen sulfide through the cooled solution until no more hydrogensulfide is absorbed. Thereafter, the alcohol, hydrogen chloride, andexcess hydrogen sulfide may be removed and the crude reaction producthydrogenated to the thiol in the presence of a sulfactive hydrogenationcatalyst. Other means of forming thioaldehydes include reaction of analdehyde with phosphorus pentasulfide and reaction of a 1,1 dihalidewith an aklali hydrosulfide. The thioaldehydes in many cases react withhydrogen sulfide to form sulfhydrates-compounds having the grouping Inhydrogenating the preformed thioaldehyde or other reaction product ofaldehydes with hydrogen sulfide to the corresponding thiol, theconditions employed are the same as those described for the combinedformation and hydrogenation of the thioaldehyde except that the presenceof hydrogen sulfide is not essential.

Thioaldehydes that may be hydrogenated according to this invention arethose corresponding to each of the carbonyl compounds mentioned aboveand their sulfhydrates and polymers.

This invention constitutes a useful and economical process for preparingprimary thiols.

These products are useful as intermediates for the preparation of otherorganic sulfur compounds such ,as sulfides,-sulfox;ides, sulfones,sulfinic and sulfonic acids and thioacetals. The compounds are alsouseful as insecticides, dyestufi' intermediates, and rubber chemicals.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that we do not limit ourselves to the specific embodimentsthereof except as defined in the appended patent claims.

We claim:

1. The process for the preparation of thiols which comprises reacting analdehyde with hydrogen and a substance selected from the groupconsisting of elementary sulfur, hydrogen sulfide and compounds capableof yielding hydrogen sulfide under the condition of reaction in thepresence of a sulfactive hydrogenation catalyst, at a temperature inexcess of 100 C.

2. The process for the preparation oi. thiols which comprises reactingan aliphatic aldehyde with hydrogen and a substance selected from thegroup consisting of elementary sulfur, hydrogen sulfide and compoundscapable of yielding hydrogen sulfide under the conditions of reaction inthe presence of a sulfactive hydrogenation catalyst, at a temperature inexcess of 100 C.

3. The process in accordance with claim 2 characterized in that thealiphatic aldehyde is a saturated aliphatic aldehyde.

4. The process for the preparation of thiols which comprises reactingan.unsaturated aldehyde with hydrogen and a substance selected from thegroup consisting of elementary sulfur, hydrogen sulfide and compoundscapable of yielding hydrogen sulfide under the conditions of reaction inthe presence of a sulfactive hydrogenation catalyst, at a temperature inexcess of 100 C.

5. The process in accordance with claim 4 characterized in that theunsaturated aldehyde is an unsaturated aliphatic aldehyde.

6. The process for the preparation of thiols which comprises reacting anaromatic aldehyde 10 with hydrogen and a substance selected from thegroup consisting of elementary sulfur, hydrogen sulfide and compoundscapabl of yielding hydrogen sulfide under the conditions of reaction inthe presence of a sulfactive hydrogenation catalyst, at a temperature inexcess of C.

7. The process which comprises reacting an aldehyde with hydrogen and asubstance selected from the group consisting of elementary sulfur,hydrogen sulfide and compounds capable of yielding hydrogen sulfideunder the conditions of reaction in the presence of a metal sulfidehydrogenation catalyst, at a temperature in excess of 100 C.

8. The process in accordance with claim 7 characterized in that themetal sulfide catalyst is obtainable by treating a finely divided activemetal with a. sulfiding agent selected from the group consisting ofsulfur, hydrogen sulfide and carbon bisulfide.

9. The process in accordance with claim 7 characterized in that themetal sulfide catalyst contains a metal polysulfide that has beentreated at an elevated temperature with hydrogen.

'10. The process in accordance with claim '7 characterized in that themetal sulfide catalyst contains metal polysulfides obtainable byprecipitation of a soluble iron group metal salt with a substanceselected from the group consisting of alkali sulfides and polysulfides,alkaline earth sulfides and polysulfides, and ammonium sulfide andpolysulfide.

11. The process in accordance with claim 7 characterized in that themetal sulfide catalyst contains molybdenum sulfide.

12. The process in accordance with claim 7 characterized in that themetal sulfide catalyst contains sulfides of the metals of the iron groupof the periodic table.

13. Process of claim 4 characterized in that the unsaturated aldehyde isan alpha, beta-unsaturated aldehyde.

14. The process of claim 7 characterized in that the metal sulfidecatalyst is cobalt sulfide.

15. As a new composition of matter 2-ethylhexanedithiol-1,3.

MARK W. FARLOW. FRANK K. SIGNAIGO.

